Expectant mothers were charged between 300 and 500 yuan (US$44 to US$74) for the information, which was provided by the sister. Neither she nor her brother, whose principal role was driving the vehicle, were named in the report.

Determining the sex of an unborn baby is illegal in mainland China. Under the one-child policy, which came to an end last year, male children were strongly favoured and female foetuses would often be aborted.

Local police had been alerted to the couple’s activities and moved in to arrest them as the woman was conducting a consultation. A search of the vehicle yielded a notebook containing 40 telephone numbers and addresses, the report said, without elaborating.

The two suspects were detained pending a full investigation, it said.

On China’s mainland it is illegal even for doctors to reveal the sex of unborn children, though the practice does go on, especially in private hospitals, the report said.

According to official figures, China had 30 million more males than females last year. Such a discrepancy has led to demographic experts discussing the feasibility of “importing” females from other countries.